A hot air balloon caught fire and crashed in a recreational vehicle park and campground Friday evening, injuring as many as 12 people, police and a witness said. Two other people were unaccounted for. The cause of the accident was not known. Weather conditions were clear at the time of the sunset flight. At least three 9-meter recreational vehicles caught fire, said Don Randall, a witness who lives in the trailer park. No one was reported hurt in those blazes. Witnesses said passengers screamed and jumped to the ground as the balloon's basket caught fire. The balloon reportedly took off from a grassy field with 12 passengers. "The thing went up about 400 feet in the air at which point it melted enough of the balloon - it collapsed," said Randall, who saw the balloon as it was on its way up and took pictures of the fiery scene. "The basket was basically a fireball, it just dropped like a stone."